Overview
This lecture introduces the classification, structure, and function of joints in the human body, along with basic joint movements.
Joint Classifications
- Joints can be classified by function (mobility) or structure (tissue type).
- Functional classifications: synarthroses (immovable), amphiarthroses (slightly movable), diarthroses (freely movable).
- Structural classifications: fibrous joints, cartilaginous joints, synovial joints.
Fibrous Joints
- Fibrous joints consist of dense connective tissue and lack a joint cavity.
- Types: sutures (skull only), syndesmoses (ligaments, e.g., tibia and fibula), gomphoses (tooth in socket).
- Sutures ossify over time, forming synostoses.
- Gomphoses involve the periodontal ligament anchoring teeth.
Cartilaginous Joints
- Cartilaginous joints connect bones with cartilage and lack a joint cavity.
- Synchondroses contain hyaline cartilage (e.g., epiphyseal plates, first rib to sternum).
- Symphyses are made of fibrocartilage, acting as shock absorbers (e.g., intervertebral discs, pelvis).
Synovial Joints
- Synovial joints have a fluid-filled cavity and are usually freely movable.
- Articular cartilage covers bone ends; joint cavity contains lubricating synovial fluid.
- Synovial membrane and fibrous layer form the articular capsule.
- Additional structures: reinforcing ligaments, menisci (fibrocartilage discs), bursae and tendon sheaths reduce friction.
Movements at Joints
- Nonaxial movement: slipping (e.g., wrist bones).
- Uniaxial, biaxial, and multiaxial movement: motion in one, two, or three planes.
- Gliding: flat bone surfaces slide over each other.
- Angular movements: flexion (decreases joint angle), extension (increases angle), hyperextension (beyond straight), abduction (away from midline), adduction (toward midline), circumduction (circular movement).
- Rotation: bone turns around its own axis (e.g., hips, shoulders).
- Special movements: supination/pronation (forearm), dorsiflexion/plantar flexion (foot), protraction/retraction (jaw).
Key Terms & Definitions
- Joint — area where two bones meet, allowing for movement.
- Synarthroses — immovable joints.
- Amphiarthroses — slightly movable joints.
- Diarthroses — freely movable joints.
- Fibrous Joint — joint held by dense connective tissue, little movement.
- Cartilaginous Joint — joint held by cartilage, limited movement.
- Synovial Joint — joint with fluid-filled cavity, high mobility.
- Suture — immovable fibrous joint in the skull.
- Syndesmosis — fibrous joint joined by ligaments.
- Gomphosis — peg-in-socket fibrous joint (tooth and socket).
- Synchondrosis — cartilaginous joint with hyaline cartilage.
- Symphysis — cartilaginous joint with fibrocartilage.
- Meniscus — fibrocartilage disc in synovial joints.
Action Items / Next Steps
- Review notes on bone structure and joint types.
- Prepare for upcoming lecture on muscle anatomy and function.